The invention relates to optical data storage devices. More specifically, the invention relates to an apparatus and method for writing data to an optical storage medium such as a digital video disc or compact disc.
An optical storage disc can store large amounts of data. A single compact disc ("CD") can store more than 500 megabytes of data, and a single Digital Video Disc ("DVD") following a DVD Rewritable ("DVD+RW") format can store more than 3 gigabytes of data. A record album could be stored on the CD; a full-length movie (compressed) could be stored on the DVD.
"Read/write" drives can write new data to "read/write" discs. Read/write discs include optical discs that allow new data to be written only once and optical discs that allow new data to be written many times. A DVD+RW disc is an example of a read/write disc that allows new data to be written many times.
A read/write drive typically has a read mode of operation and at least one of the following write modes of operation: a write-append mode and an insert-edit mode. The write-append mode allows new data to be appended to previously written data on the read/write disc, and the insert-edit mode allows previously written data to be overwritten with new data.
When writing new data to a read/write disc, it is not desirable to create a frequency or phase discontinuity between the previously written data and the new data. The read/write drive might not be able to tolerate such discontinuities during read back of the previously written data and the new data. During readback, the discontinuities might cause problems for clocks and data recovery circuitry. Consequently, the phase discontinuities might render portions of the read/write disc effectively unreadable by the read/write drive.
This phase discontinuity problem is typically overcome by the use of "edit gaps" (also known as a "splice areas"). New data is written to a read/write disc in blocks that are separated by the edit gaps. The edit gaps allow sufficient time for the clocks and data recovery circuitry to recover from a phase discontinuity before data is read from the next block.
However, the use of edit gaps has its drawbacks. Storage capacity of the read/write disc is reduced because data is not stored in the edit gaps.
Moreover, the edit gaps might render portions of the read/write disc unreadable by existing read-only drives. Older read-only drives that were developed prior to newer generation read/write drives may not be capable of processing edit gaps. Unless an existing read-only drive is somehow modified to navigate past the edit gaps, it will have difficulty reading the data stored on the read/write disc.
A need exists for reducing phase discontinuity between the new data and previously written data without the use of edit gaps.